Amplifier for centimeter waves



Nov. 4, 1952 K. s. KNOL ETAL 2,616,990

AMPLIFIER FOR CENTIMETER WAVES Filed Dec. 26, 1947 &

IN VEN TOR.

azflmumwmaz BY ME?! mama AGENT Patented Nov. 4, 1952 AMPLIFIER FOR CENTIMETER WAVES Kornelis Swier Knol' and Aldert van der Ziel, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford,

Conn.,as trustee Application December 26, 1947, Serial No. 794,052 In the Netherlands January 13, 1947 It is known to use for the amplification of waves of the order of magnitude of centimetres a "tube comprising a helical conductor, along which the waves required to be amplified advanoeywh'ilst along the axis of the helix passes an electron-beam, the electrons of which exhibit a velocity which is so chosen, with respect to the velocity of the advancing waves measured in the direction of the coil axis that the electrons give off energy to the advancing waves, so that the latter appear, at the end of the helix, asamplified waves.

The waves required to be amplified are fed in this case to that end of the helix which is nearest to the source of electrons, whilst the pitch .of the helix and/or the diameter of the turns, as well as the voltages used for producing the electron-beam are so chosen that the speed of propagation of the waves "measured along the axis of the helix, is slightly less than the mean speed of the electrons of the beam. Under these conditions the electrons give off energy to the waves, so that the latter may be taken as amplified waves from that end of the helix which is remote from theelectron source.

"In order to avoid the production of stationary Waves 'on the helix, it is necessary to close the latter at the output end by means of an impedance matched to the helix. Since, however, it is not'possible in this manner completely to avoid reflections at the output end of the'helix, it has, moreover-proved necessary to give the electrical resistance of the helix a comparatively high value. This step naturally has a detrimental V effectpn the amplification to be obtained, since losses occur in the resist-ancematerial.

The principal object of the invention is to provide an'i-mproved travelling wave tube amplifying system. More specifically, it is an object of this invention-'to provide a travelling wave tube amplifying system in which wave reflections are minimized. a I

The invention is based on the recognition that reflections maybe avoided to a sufficient extent even if the'helix does not consist of resistance material, provided the total amplification is not excessively highand consequently, the helix is chosen to be comparatively short. According to the invention, in order to ensure nevertheless proper amplification, the helix, which otherwise exhibits a large number of turns, consists of two ormore separate parts, each ,ofwhich is traversed in succession by thebeam of electrons, whilst the output voltage. is taken from that end of the 6 Claims. (Cl. 179-171) helix finally traversed by the electron beam which is remote from the electron source.

Since the amplification in each part is comparatively small, the reflections occurring therein are little troublesome. Since moreover, the electron beam successively traverses the various parts so that they all contribute to the amplification, a comparatively high amplification is nevertheless obtained, since the number of parts may be chosen arbitrarily large. The reflections may be counteracted by closing the helices, at the ends remote from the source of electrons by means-of a suitably chosen impedance. First, the velocity of the electron beam may be modulated, which may be efiected' by means of a helix in which the ratio between the pitch and the diameter is so chosen that the speed of propagation of the wave measured along the axis of the helix is substantially equal to the velocity of the electrons. This helix is, in this case, first traversed by the beam of electrons, the wave amplification occur-ing therein being only slight. It is also possible, however, to construct all parts in such manner that in each of them the amplification of the advancing Wave occurs.

If, neverthelesathe reflections should :prove to be annoying, the last. few turns of at least. one of the parts may be made of: resistance material or may be coated therewith, it being thus ensured that in the afirst part of the helix the amplitude of the wave retains a comparatively high value of andthat a tavourable. signal noise ratio is maintained.

In order that the invention may be more clearly understood and readily carried into effect, it will now bedescribed more fully with reference to, 'the'accompanyin-g drawing, which shows, by way of example, two embodiments thereof.

In the drawing: 1 .Fig, .1 is a schematicdiagram of afirstpreferredtembbdimentof the invention; and

Fig. 2 is a schematic diagram of a second preferred embodiment of the invention.

velope :of a tube within which a device 2 for producing a beam of electrons is arranged in such manner that the beam travels along the axis of the tube .and, for example, may be intercepted by. an electrode 3. The beam traverses a number of similar helices .8, 9,, and ill of a material exhibiting a satisfactory conductivity at high frequencies. It is possible, as an alternative, to manufacture these helices of material of comparatively poor conductivity and to. coat. them In Fig. .1 of the drawing, 1 designates the en- I 3 with material of satisfactory conductivity. The ends of each of the helices are taken to the outside. That end of the helix 8 which is located nearest to the electron-source, is connected to earth through an impedance 4. The voltages required to be amplified, which occur at terminals II, are supplied to this impedance. The other end of the helix 8 is earthed through an impedance which is equal to the surge impedance of the helix.

That end of the second helix 9 which is nearest to the electron-source, maybe connected to earth through an impedance or not, aswell as the end of the helix l0 nearest to the electronsource. The other ends of the helices 9 and I!) are earthed through impedances 6 and l respec-v tively. These impedances are again matched to the surge impedances of the corresponding helices. The amplified voltages may be taken from the impedance 1.

The number of helices successively traversed by the electron-beam may be chosen at will. By carrying out the invention it is thus possible to obtain with a single tube a high amplification without production of troublesome reflections which may give rise, inter alia, to self-oscillation.

Fig. 2 represents an amplifier which differs from that shown in Fig. 1 in that there are only two helical parts l3 and M of which the former is wound in such manner that the mean velocity of the electrons slightly differs from the speed of propagation of the waves along the coil. Only slight amplification consequently occurs in this part but the electron-beam acquires a certain velocity modulation which, in the further movement of the beam, is converted into intensitymodulation. In the part I4 the velocityand/or intensity-modulation beam generates a wave which, at the end of the part I4, is taken as an amplified wave from the impedance 1.

Owing to the fact that in part 13, only-slight amplification occurs, the production of reflections is here practically not troublesome. The reflections in the second part M are also little troublesome, since this part may be comparatively short, at least much shorter than with the use of resistance material. The part l4 in Fig. 2 may also be coated with resistance material or be made thereof, if it is desired to counteract the reflections to a still higher extent.

Alternatively, instead of a single helix Hi there may be provided, a plurality of such helices which are all successively traversed by the beam as in Fig. 1, with the result that cascade amplification is obtained.

What we claim is:

1. Amplifying apparatus for high-frequency oscillations comprising a traveling-wave electron beam tube including a helical conductor for guiding oscillations, an input terminal to supply the oscillations to be amplified to one end of said conductor, an output terminal to derive the amplified oscillations from the other end of said conductor, an electron beam'source adjacent'the input end'of said conductor and a collector electrode adjacent the output end of said conductor, said source being arranged to direct the electron beam along the axis of said helical conductor towards said collector electrode with a velocity which at any point thereon exceeds that of the traveling wave of said oscillations as measured alongsaid axis, said helical conductor being constituted by a plurality of separate sections which are successively traversed by said beam, and a like plurality of impedance elements each con- 4 nected to a respective section of said conductor at the end thereof remote from said source and having a value acting to suppress reflections in the associated section.

2. An arrangement, as set forth in claim 1, wherein each of said impedance elements has a value corresponding to the surge impedance of the associated section.

3. In a traveling-wave electron beam tube for the amplification of high-frequency oscillations, the combination comprising a helical conductor for guiding oscillations, input means to supply the oscillations to be amplified to one end of the conductor, output means to derive the amplified oscillations from the other end of said conductor, an electron beam source adjacent the input end of said conductor, and a collector electrode adjacent the output end of said conductor, said source being arranged to direct the electron beam along the axis of said helical conductor towards said collector electrode with a velocity which at any point thereon exceeds that of the traveling wave of said oscillations as measuredalong said axis, said helical conductor being constituted by two separate sections which are successively traversed by said beam, the section of said conductor adjacent said source having a ratio between the pitch and diameter thereof such that the velocity of the traveling wave thereon is greater than the velocity in the other section.

4. A traveling-wave tube, as set forth in claim 1, wherein the turns in the rear portion of at least one of said sections have a resistance which is high relative to the remaining turns in said section.

5. Amplifying apparatus for high-frequency oscillations comprising a traveling-wave electron beam tube including a helical conductor for guiding oscillations, an input terminal to supply the oscillations to be amplified to one end of said conductor, an output terminal to derive the amplified oscillations from the other end of said conductor, an electron beam source adjacent the input end of said conductor and a collector electrode adjacent the output end of the conductor, said source being arranged to direct the electron beam along the axis of said helical conductor towards said collector electrode with avelocity which at any point thereon exceeds that of the traveling wave of said oscillations as measured along said axis, said helical conductor being constituted by a plurality of separate sections which are successively traversed by said beam, an input impedance having one end thereof connected to the input terminal of said tube, means to impress the oscillations to be amplified across said input impedance, and a like plurality of matching impedance elements each having one end thereof connected to a respective section of said conductor at the end thereof remote from said source, the other ends of said matching elements being connected to the other end of said input impedance, and means to derive the amplified oscillations from across the matching impedance connected to the output terminal of said tube.

6. Amplifying apparatus for high-frequency oscillations comprising atravelingwave electron beam tube including within an evacuated envelope a helical conductor for guiding oscillations,

an input terminal to supply the oscillations to be amplified to one end of said conductor, an output terminal to derive the amplified oscillations from the other ,end of said conductor, an electron gun structure adjacent the input end of said conductor and the collector electrode adjacent the output end of the conductor, said gun structure being arranged to project an electron beam along the axis of said helical conductor towards said collector electrode with a velocity which at any point thereon exceeds that of the traveling wave of said oscillations as measured along said axis, said helical conductor being constituted by a plurality of separate sections which are successively traversed by said beam, an input impedance having one end thereof connected to the input terminal of said tube, the oscillations to be amplified being impressed across said input impedance, and a like plurality of matching impedance elements each having one end thereof connected to a respective section of said conductor at the end thereof remote from said source, the other ends of said matching impedances being connected to the other end of said input impedance, the amplified oscillations being derived from the matching impedance connected to the output terminal of said tube, the matching elements each having a value corresponding to the surge impedance of the associated section.

KORNELIS SWIER KNOL. ALDERT VAN DER ZIEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Article entitled "Wideband Microwave Amplifier Tube, pp. -92 incl., Electronics for Nov. 1946, X2'50-27.5 (T.W.). 

